Adjustment arrangement of an optical element

ABSTRACT

A arrangement serves for the adjustment of an optical element ( 1 ), in particular of a lens in an optical system, in particular in a projection lens system for semiconductor lithography. The optical element ( 1 ) is mounted in a mount ( 3 ) by means of a number of bearing feet ( 2 ) distributed over the circumference of the optical element ( 1 ) and is selectively deformable by actuators ( 5 ). At least some of the bearing feet ( 2 ) are engaged by the actuators ( 5 ) in a region of the respective bearing foot ( 2 ) in such a way that the respective bearing foot ( 2 ) can be displaced in the direction of the optical axis ( 7 ).

The invention relates to an adjustment arrangement of an opticalelement, in particular of a lens in an optical system. The inventionalso relates to a projection lens system in semiconductor lithographywith a number of optical elements and with at least one adjustmentarrangement for an optical element.

EP 1 014 139 A2 discloses an optical system for comparable purposes, inwhich an optical element, in particular a lens, is mounted on amultiplicity of angular bearing feet arranged in a uniformly distributedmanner over the circumference of an inner ring or a mount. These bearingfeet have the effect of providing on the one hand precise mounting andon the other hand appropriate elasticity for introducing deformationsonto the lens as the optical element. The deformations are in this caseapplied to an inner ring of a mount that is connected to all the bearingfeet and are transferred through the bearing feet to the region of theoptical element.

However, it is a disadvantage of this arrangement that the specificdeformation of the optical element is made more difficult by thedistortions of the inner ring, which cannot be sufficiently predicted ineach case, influencing the deformations that are to be transferred tothe lens. The deformations of the inner ring are passed on to theoptical element via a certain number of the bearing feet that arepresent. To distort the optical element in a specific way, it would haveto be known exactly how the inner ring reacts to the respectivedistortions and how the latter are transferred to the optical elementfrom the region of the inner ring and by which of the bearing feet.

Since, however, these effects cannot be calculated with the requiredaccuracy and cannot be reproducibly repeated, this represents adisadvantage of such a construction, since the specific, punctiformtransfer of deformations to the optical element is adversely affected bythe construction in a way which cannot be reproduced.

For further prior art, reference is made to U.S. Pat. No. 4,993,823, WO99/67683, U.S. Pat. No. 6,552,862 B2 and U.S. Pat. No. 6,580,570.

Incorporated by reference are U.S. Pat. No. 6,307,688, U.S. Ser. No.10/002,097 and U.S. Ser. No. 10/661,183.

It is therefore the object of the present invention to provide aarrangement for the passive and active adjustment of an optical elementwhich, apart from the required precise mounting and the simultaneouslydesired elasticity of the mounting, also allows the selectiveintroduction of deformations into the region of the optical element.

This object is achieved according to the invention in the case of anadjustment arrangement of an optical element, in particular of a lens inan optical system, the optical element having a circumference and beingmounted in a mount by a number of bearing feet arranged in a distributedmanner over the circumference of the optical element, the opticalelement being selectively deformable by actuators, and at least some ofthe bearing feet being engaged by at least one actuator in such a waythat the respective bearing foot can be displaced in a directionsubstantially orthogonal to said circumference.

The fact that the actuators engage in the region of the respectivebearing foot in such a way that they displace the bearing foot itself,and consequently deform the optical element, allows very specificintroduction of the desired deformations into the optical element to beachieved without this process being affected by the often unreproducibleeffects which could occur, for example, in the case of deformation of aninner ring of the mount.

It is for instance possible in a particularly advantageous way toachieve a deformation of the optical element by means of a force,without thereby changing the position of said element, by introducingthe forces into the bearing feet. This is made possible by the pinpointengagement in the region of the bearing feet, so that deformation andmanipulation can be adjusted or regulated in relation to one another insuch a way that they can be monitored.

In a particularly favorable development of the invention, the number ofbearing feet is in this case significantly reduced in comparison withthe prior art, since now the deformations are introduced into theoptical element via the bearing feet themselves, and it is consequentlypossible to dispense with uniform fastening of the optical elements toan inner ring of a mount transferring the deformation. In this way, thenumber of bearing feet (for example 8, 12 or 16), which requirecomparatively great expenditure for their production and adjustment, issignificantly reduced and the resting of the lens, on fewer bearing feetaltogether, is improved with regard to the possibility of active,semi-active and passive adjustment.

Furthermore, the arrangement may be formed in such a way that, in aparticularly favorable development of this idea, only some of thebearing feet, for example every second one, or bearing feet arranged atan appropriate angle in relation to one another, for example every 90°,are formed as bearing feet that can be manipulated. In this way theexpenditure with regard to the actuators can be further reduced, thespecific introduction of the deformation through the respective bearingfeet themselves having the effect that the possibility of deforming theoptical element is nevertheless improved in comparison with the priorart, since a more specific introduction of force takes place.

The adjustment arrangement according to the invention may be provided inan advantageous way in the case of an optical element that is providedin a projection lens system in semiconductor lithography, such as forexample a lens.

For precise mounting, in particular low-deformation mounting, along withappropriate elasticity, the bearing feet may be appropriately adapted.For this purpose, they may be formed for example as solid joints, whichmay be formed for example in a U-shaped manner. For specific deformationof the optical element, actuators may then engage the bearing feet, forexample where they are formed as solid joints.

Further advantageous configurations of the invention emerge from theremaining subclaims and the exemplary embodiments, which are explainedbelow on the basis of the drawing, in which:

FIG. 1 shows a representation of the principle of a constructionaccording to the invention with an actuator indicated in principle;

FIGS. 2 a and 2 b show possible embodiments of an actuator in aconstruction according to FIG. 1;

FIG. 3 shows an alternative embodiment of an actuator in a constructionaccording to FIG. 1;

FIG. 4 shows an alternative possibility for the configuration of abearing foot;

FIG. 5 shows a further alternative embodiment of the configuration of abearing foot;

FIG. 6 shows an enlarged representation of the region VI from FIG. 5;

FIG. 7 shows a representation of the principle of a possible arrangementof manipulable bearing feet and fixed bearing feet;

FIG. 8 shows an alternative possibility for arranging manipulablebearing feet and fixed bearing feet;

FIG. 9 shows a further alternative possibility for arranging manipulablebearing feet and fixed bearing feet; and

FIG. 10 shows a projection exposure machine with a projection lenssystem.

FIG. 1 shows an optical element 1, here a lens, which is mounted in amount 3 by means of bearing feet 2. The bearing feet 2 are formed in anapproximately L-shaped manner and are connected at their one leg 2 a tothe mount 3. At the free end of their other leg 2 b, they have a bearingsurface 4 for the optical element 1.

The bearing feet 2 are made with a comparatively small wall thickness,so that they have a certain intrinsic elasticity, which permits mountingof the optical element 1 in the mount 3 that is as ideal as possible andinitially without any deformation, it being possible for the componentreferred to here as the mount 3 also to represent merely an inner ringof a mount that can be manipulated with respect to an outer ring.

The optical element 1 thus initially mounted without any deformation isthen to be deformed in a way corresponding to the requirements of theoptical system, in particular a lens system for semiconductorlithography, which is not represented in its entirety. For example, itmay be meaningful to impress an astigmatism on the optical element 1.For this purpose, actuators 5, which are indicated in principle here byan arrow, are provided at least in the case of some of the bearing feet2.

The actuator 5 is arranged in the region of a holding element 6, whichis firmly connected to the mount 3, and in this way acts on the leg 2 bof the bearing foot 2 having the bearing surface 4.

The arrow symbolizing the actuator 5 in this case points in bothdirections, although one direction is undoubtedly generally adequate forthe action of the force, depending on the type of actuator 5, since theother direction of the force is realized by the force of gravity exertedby the optical element 1.

If all, or at least some, of the bearing feet 2 are then provided withsuch an actuator 5, the optical element 1 can be manipulated or deformedin this region by the respective actuator 5 in a direction orthogonal tothe circumference which is mostly the direction of the optical axis 7,which in optics is generally referred to as the z direction.

In principle, it would undoubtedly be desirable here to achieveexclusive deformation of the optical element 1, without the opticalelement 1 thereby being changed in its position with regard to theoptical axis 7, that is to say manipulated, by appropriate exposure ofthe individual bearing feet 2 to the appropriate forces. The possibilityof providing the respective bearing feet 2 with the respective actuator5 and in this way being able to introduce an appropriate direction offorce virtually in every region of the optical element 1 allows such ameaningful deformation of the optical element 1 to be achieved.

FIG. 2 a then shows an actual exemplary embodiment of one of theactuators 5, as already mentioned above in principle.

The actuator 5 is in this case configured as a pneumatic or hydraulicactuator 5 a, that is to say is actuated by means of a pressure p. Here,too, the force of the weight exerted by the optical element 1 again actsas the restoring force.

The introduction of the force into the optical element 1 takes place bychanging the pressure p, which is directed via a feed line 8 in theholding element 6 to a bellows 9 arranged between the holding element 6and the one leg 2 b of the bearing foot 2. Depending on the pressure pintroduced, appropriate manipulation of the respective bearing foot 2 isobtained with the actuator 5 a, and this in turn then brings about adeformation of the optical element 1 in precisely the region in whichthe bearing foot 2 is arranged.

FIG. 3 shows a further possibility for the configuration of the actuator5.

The actuator 5 in the exemplary embodiment represented in FIG. 3comprises an actuating screw 10, which acts on the leg 2 b of thebearing foot 2 via a spring element 11. Here, too, the restoring force,against the force of the spring, is in turn applied by the force of theweight of the optical element 1.

In principle, it would in this case be possible in the exemplaryembodiment represented here to configure the actuator 5 merely as anadjusting element, that is to say to use the actuating screw 10 forpassive adjustment. As an alternative to this, it would of course alsobe possible here to provide the actuating screw 10 with an appropriatedrive, for example a motor drive, in order to permit a semi-activepossibility of adjustment in the form of an actuator during theoperation of the optical system.

FIG. 4 then shows another embodiment of the bearing foot 2. The bearingfoot 2 is formed here in one piece with the mount 3, which is alsopossible in principle in the case of the exemplary embodiments alreadymentioned above, but is not necessary there.

Here, the bearing foot 2 comprises a lever element 2 c, which isconnected by means of two solid joints 12 on one side to the mount 3 andon the other side to a part 2 d of the bearing foot 2 that carries thebearing surface 4.

Since the solid joints 12 are spaced apart from each other by the widthof the lever element 2 c, there is the possibility of realizing adisplacement of the part 2 d, and consequently of the bearing surface 4,in the direction of the optical axis 7 when there is a deflection of thelever element 2 c in a direction perpendicular to the optical axis 7.

In the exemplary embodiment represented in FIG. 4, this is achieved byan actuating screw 10 as the actuator 5, which engages on the side ofthe lever element 2 c remote from the solid joints 12. The movement ofthe lever element 2 c can be achieved by means of the actuating screw10. This movement of the lever element 2 c is thereby transferred in amonitored manner by the fastening of the lever element 2 c by means ofthe solid joints 12 to the part 2 d of the bearing feet 2 that iscarrying the bearing surface 4, and consequently brings about theintroduction of a force into the optical element 1 that at least runsonto the optical element 1 at least approximately in the direction ofthe optical axis 7. The actuating screw 10 may in this case of courseagain engage the lever element 2 c by means of a spring element 11,which is not represented here however, or be designed as a pneumatic orhydraulic actuator.

In principle, it would of course also be conceivable and meaningful toconfigure all the actuators 5 of the exemplary embodiments presented sofar and those still to be described later in some other form, forexample as active actuators, for example by piezo elements or piezostacks, and in this way produce specific deformations of the lens 1during the operation of a lens system in which the lens 1 is installed,whereby the path of rays in the lens system can be correspondinglyinfluenced.

FIG. 2 b shows as an example a piezo stack 15, which takes the place ofthe hydraulic or pneumatic actuator 5 a according to FIG. 2 a.

As in the case of the exemplary embodiment described previously in FIG.3, here, too, it is also possible for the actuating screw 10 in turn tobe actuated actively as an actuator by means of a motor drive or thelike, so that, apart from a purely passive adjustment, a semi-activereadjustment of settling effects can also be performed during theoperating period and, if appropriate, active control of the deformationof the optical element 1 can also be performed during actual operation.

As also already in the case of the exemplary embodiments describedabove, the force of the weight of the optical element 1 acts here as therestoring force, so that it is ensured by the force of the weight thatthe lever element 2 c is always pressed against its actuator 5, so thata direct manipulation of the lever element 2 c is possible.

FIG. 5 then shows a further embodiment of the bearing foot 2, which inprinciple corresponds to the construction just described in FIG. 4 withthe lever element 2 c. However, the bearing foot 2 is in this caseformed in a U-shaped manner, one leg 2 e of the U-shaped bearing foot 2being connected to the mount 3. This connection may either be realizedagain as a one-piece configuration of the bearing foot 2 with the mount3 or it is also conceivable that, as represented here, the bearing foot2 is connected to the mount 3 by means of appropriate connectingtechniques, such as welding, adhesive bonding, screwing or the like.

The other leg 2 f of the bearing foot 2 that is formed in a U-shapedmanner carries on its side remote from a base element 2 e the part ofthe bearing foot 2 that is designated by 2 d and is connected to theoptical element 1 via the bearing surface 4. To create a definedmovement of the part 2 d of the bearing foot 2 for the operation stillto be explained in detail below, the at least one solid joint 12 isarranged between the part 2 d and the leg 2 f of the bearing foot 2.

By means of an actuating screw 10, which together with a motor drive 13indicated in principle here, for example an electric motor, forms theactuator 5 in the form of an actuator 5 a, the region of the base 2 g ofthe bearing foot 2 can be displaced in a direction at leastapproximately perpendicular to the optical axis 7. The construction ofthe bearing foot 2 in its U-shaped configuration, which may also beregarded as a slotted lever, then brings about the effect of amanipulation of the part 2 d of the bearing foot 2 against the force ofthe weight of the optical element 1.

The possibilities arising from this manipulation are the same as thosealready described above.

The construction described in FIG. 5 shows the possibility in this case,however, that it permits by its configuration an ideal possibility forintroducing a stepping-up or stepping-down transmission movement of theactuator 5 a onto the movement of the bearing surface 4. At the sametime, this produces a comparatively soft construction which, when theactuator 5 a is not operated, permits mounting of the optical element 1in its starting position at least approximately without any deformation.

In order then to avoid any displacement of the optical element 1 in itsplane perpendicular to the optical axis 7, the bearing foot 2represented in FIG. 5 also has a stabilizing element 14, which is formedin the manner of a membrane or the like, so that in practice it does notimpair the movement of the bearing foot 2 or of the bearing surface 4 inthe direction of the optical axis 7, but effectively prevents themovement in the plane perpendicular thereto.

The stabilizing element 14 is represented once again in a detailed formin FIG. 6. The thickness of the stabilizing element 14 is madecomparatively thin in comparison with the thicknesses of the two legs 2f, 2 e of the bearing foot 2 and the stabilizing element 14 is connectedto the respective legs of the bearing foot 2 via two solid joints 12.

This achieves the effect that a movement in the direction of the opticalaxis 7 can take place at least approximately unhindered, while adeflection of the optical element 1 in a plane perpendicular to theoptical axis 7 is effectively prevented.

FIGS. 7, 8 and 9 show various possibilities for arranging such bearingfeet 2 that can be manipulated by means of an actuator 5 on their own ortogether with fixed bearing feet that are not provided with an actuator5.

The fact that a deformation applied to the inner ring of the mount nowno longer has to be introduced as uniformly as possible into the opticalelement 1, as in the case of the prior art, but that the bearing foot 2itself can be manipulated in order to deform the optical element 1 in aspecific way, means that far fewer bearing feet 2 than in the case ofthe prior art are now required.

In the exemplary embodiments represented here, six of the bearing feet 2are respectively represented. The bearing feet identified by the crossare intended in this case to be the bearing feet 2 that have theappropriate actuator 5 or actuators 5 a and consequently permit thepossibility of introducing a deformation into the optical element 1through a force acting in the direction of the optical axis 7.

The construction according to FIG. 7 allows three-wave (three-leafclover) deformations of the optical element 1 to be applied, while theconstruction according to FIG. 8 permits the introduction of anastigmatism in one plane.

FIG. 9 shows the most variable construction, which however also involvesthe greatest expenditure with regard to the control of the actuators 5or actuators 5 a on account of the costs arising in production. In thisconstruction, a number of deformations can be introduced into theoptical element 1 and then be superposed in the latter to form thecorresponding wave aberrations.

It would of course be quite conceivable also to realize a far greaternumber of fixed and/or manipulable bearing feet 2′, 2, for exampletwelve or sixteen manipulable bearing feet allowing a multiplicity ofwave aberrations to be produced in the optical element. In particular,however, it is meaningful if astigmatic and three-wave distortions canbe introduced, which can be ideally realized for example in anarrangement with eight or twelve bearing feet. Higher-order waveaberrations are often of secondary importance for the quality of theoptical imaging quality to be achieved. The expenditure in terms ofcosts and components could only be justified with difficulty from aneconomic viewpoint.

In FIG. 10, a projection exposure machine 16 for microlithography isrepresented in principle. This serves for exposing patterns on asubstrate which is coated with photosensitive materials, generallyconsists predominantly of silicon and is referred to as a wafer 17, forthe production of semiconductor arrangements, such as for examplecomputer chips.

The projection exposure machine 16 in this case substantially comprisesan exposure arrangement 18, a arrangement 19 for receiving and exactlypositioning a mask provided with a grid-like pattern, the so-calledreticle 20, by which the later patterns on the wafer 17 are determined,a arrangement 21 for securing, moving and exactly positioning this verywafer 17 and an imaging arrangement, to be specific a projection lenssystem 22 with a number of optical elements, such as for example lenses1, which are mounted in a lens-system housing 23 of the projection lenssystem 22 by means of mounts 3.

The basic functional principle in this case provides that the patternsintroduced into the reticle 20 are exposed onto the wafer 17 with areduction in the size of the patterns.

Once exposure has taken place, the wafer 17 is moved further in thedirection of the arrow, so that a multiplicity of individual zones, eachwith the pattern predetermined by the reticle 20, are exposed on thesame wafer 17. On account of the step-by-step advancing movement of thewafer 17 in the projection exposure machine 16, the latter is also oftenreferred to as a stepper.

The exposure arrangement 18 provides a projection beam 24, for examplelight or similar electromagnetic radiation, required for projecting theimage of the reticle 20 onto the wafer 17. A laser or the like may beused as the source for this radiation. The radiation is shaped in theexposure arrangement 18 by means of optical elements in such a way that,when it impinges on the reticle 20, the projection beam 24 has thedesired properties with regard to diameter, polarization, shape of thewave front and the like.

An image of the reticle 20 is produced by means of the projection beam24 and transferred by the projection lens system 22 in an appropriatelyreduced size onto the wafer 17, as already explained above. Theprojection lens system 22 has a multiplicity of individual refractiveand/or diffractive optical elements, such as for example lenses 1,mirrors, prisms, end plates and the like. In this case, one or morelenses 1 may be mounted in the way represented in FIGS. 1-9 anddescribed above and adjusted or deformed in order to optimize the pathof rays.

1-61. (canceled)
 62. An apparatus, comprising: a mount for positioningan optical element in an optical system, the optical system having anoptical axis and the mount comprising at least one bearing forsupporting the optical element, the at least one bearing comprising: afirst bearing part configured to contact a surface of the opticalelement and support the optical element when the optical element ispositioned in the mount; an actuator configured to adjust a forceapplied in a direction parallel to the optical axis by the first bearingpart to the surface of the optical element; and a spring configured tocouple the actuator to the first bearing part.
 63. The apparatus ofclaim 62, wherein the first bearing part is a lever comprising anengagement surface that contacts the optical element and a pivot pointopposite the engagement surface.
 64. The apparatus of claim 63, whereinthe mount comprises a frame against which the lever pivots.
 65. Theapparatus of claim 63, wherein the spring couples the actuator to thelever between the engagement surface and the pivot point.
 66. Theapparatus of claim 62, wherein the first bearing part is a U-shapedpart, and a first section of the U-shaped part contacts the surface ofthe optical element and a second section of the U-shaped part is coupledto the spring.
 67. The apparatus of claim 66, wherein the mountcomprises a frame that extends circumferentially around the opticalelement when the optical element is positioned in the mount, and a thirdsecond of the U-shaped part contacts the frame.
 68. The apparatus ofclaim 67, wherein the second section of the U-shaped part connects thefirst section to the third section.
 69. The apparatus of claim 62,wherein the spring is a coil spring.
 70. The apparatus of claim 62,wherein bearing is configured so that the weight of the optical elementcompresses the spring when the optical element is positioned in themount.
 71. The apparatus of claim 62, wherein the spring is positionedbetween the first bearing part and the actuator.
 72. The apparatus ofclaim 62, wherein the actuator comprises an adjustable screw.
 73. Theapparatus of claim 62, wherein the mount comprises a frame and theadjustable screw is set in the frame in a manner allowing adjustment ofthe screw in a direction parallel to the optical axis.
 74. The apparatusof claim 62, wherein the optical element is a lens.
 75. The apparatus ofclaim 74, wherein the surface of the lens contacted by the actuatorintersects the optical axis.
 76. The apparatus of claim 62, wherein themount comprises additional bearings, the bearings being arranged in adistributed manner over a circumference of the optical element.
 77. Theapparatus of claim 76, wherein the bearings are arranged to allowintroduction of a three-wave deformation to the optical element byactuation of the bearings.
 78. The apparatus of claim 76, wherein thebearings are arranged to allow introduction of an astigmatism to theoptical element by actuation of the bearings.
 79. The apparatus of claim76, wherein the bearings are distributed in relation to each other at anangle of 120° with respect to the optical axis.
 80. The apparatus ofclaim 76, wherein the additional bearings include adjustable bearingsand non-adjustable bearings.
 81. The apparatus of claim 80, wherein thebearings are arranged so that the adjustable bearings alternate with thenon-adjustable bearings over the circumference of the optical element.82. The apparatus of claim 80, wherein the bearings include threeadjustable bearings and three non-adjustable bearings.
 83. A projectionlens system for a microlithography exposure machine, comprising: aplurality of optical elements; and a mount for positioning one of theoptical elements in the projection lens system, the projection lenssystem having an optical axis and the mount comprising at least onebearing for supporting the optical element, the at least one bearingcomprising: a first bearing part configured to contact a surface of theoptical element and support the optical element when the optical elementis positioned in the mount; an actuator configured to adjust a forceapplied in a direction parallel to the optical axis by the first bearingpart to the surface of the optical element; and a spring configured tocouple the actuator to the first bearing part.
 84. The projection lenssystem of claim 83, wherein the mount comprises additional bearings, thebearings being arranged in a distributed manner over a circumference ofthe optical element.
 85. The apparatus of claim 84, wherein theadditional bearings include adjustable bearings and non-adjustablebearings.
 86. The apparatus of claim 85, wherein the bearings arearranged so that the adjustable bearings alternate with thenon-adjustable bearings over the circumference of the optical element.87. The apparatus of claim 85, wherein the bearings include threeadjustable bearings and three non-adjustable bearings.
 88. A method,comprising: providing an optical system comprising an optical elementpositioned by a mount having at least one adjustable bearing supportingthe optical element; and adjusting a force applied in a directionparallel to the optical axis by the bearing to a surface of the opticalelement, wherein the bearing comprises a first bearing part thatcontacts contact the surface of the optical element and supports theoptical element, an actuator, and a spring that couples the actuator tothe first bearing part, and the force applied to the optical element bythe bearing is adjusted by adjusting the actuator.